Crystal structure and magnetocaloric effect of DyGa2 and DyGa1.8Cu0.2 compounds

The crystal structures and magnetocaloric effect of DyGa2 and DyGa1.8Cu0.2 compounds were studied by X-ray powder diffraction and magnetic measurements. The main results show that the crystal structures of compounds are hexangular structure with space group of P6/mmm, and the cell volume decreases when Ga atoms are substituted by Cu atoms. The Neel temperatures of DyGa2 and DyGa1.8Cu0.2 are 16 and 113 K, respectively. They are anti-ferromagnetic below Neel temperature, which become paramagnetic near Neel temperature. The kind of this phase transiton is second order phase transition. The M vs. H curves for T&le8 K exhibit features that resemble those of a metamagnetic transformation which is first order phase transition. For a magnetic field change of 50 kOe, the maximum values of -??SM for DyGa2 is 7.3 J&middotkg-1&middotK-1, and cooling power is 131 J&middotkg-1. The values of -??SM for DyGa2 is unconventionally negative (-14.9 J&middotkg-1&middotK-1) at about 5 K. The phenomenon can be used in temperature control. A small amount of Cu doping makes the magnetic refrigeration temperatures to about 100 K. They are potential candidates for the practical magnetic refrigeration.EI0SUPPL. 135-394